Some storage devices each have a large storage capacity provided by connecting multiple memory devices to one another via, for example, expander modules. An example of an expander module is an SAS expander, and examples of the memory device are an HDD and an SSD. Hereinafter, a memory device is sometimes referred to as a disk.
The term “SAS” is an abbreviation for Serial Attached SCSI; the term SCSI is an abbreviation for Small Computer System Interface. The term “HDD” is an abbreviation for a Hard Disk Drive, and the term “SSD” is an abbreviation for Solid State Drive.
Such a storage device includes a Drive Enclosure (DE) that includes multiple disks and an SAS expander, and a controller module (CM) that controls the DE. The multiple disks in the DE are connected to the CM via the SAS expander.
The SAS expander is provided with multiple SAS ports (PHYs). The multiple SAS ports include an upper connection port connected to the CM or an SAS port of an upper DE and a lower connection port connected to the upper connection port of a lower DE. Two SAS ports are connected to each other through an SAS cable.
[Patent Literature 1] Japanese Laid-open Patent Publication No. 2002-118563
[Patent Literature 2] Japanese Laid-open Patent Publication No. 2002-163049
Some recent SAS expanders (expander chips) are provided with a function of Wake on SAS. An SAS expander with the function of Wake on SAS automatically turns on and off the power source for the DE in synchronization with a link-up state of the upper connection port. For this purpose, the firmware of the SAS expander monitors, for example, the link-up state of the upper connection port. Upon detection of continuing a link-down state of all the upper connection ports for a predetermined time period (e.g., two seconds), the firmware switches the power supply to the disks and the expander chip in the DE to a consumption-power saving mode (Low Power), so that the power supply to the DE can be made into a state of being close to zero.
After being switched into the consumption-power saving mode by the above function of Wake on SAS, the SAS expander keeps only the activation interruption receiver that receives, as activation interruption, an SAS packet (Out Of Band: OOB) for restoring the power supply state to a normal power supply mode to a resident state (i.e., in a state of turning on the power supply). Then, the SAS expander turns off the power supply to the parts and elements in the DE except for the activation interruption receiver. Examples of the parts and elements in the DE except for the activation interruption receiver correspond to the multiple disks and the elements and parts in the SAS expander except for the activation interruption receiver.
The activation interruption receiver interrupts the SAS expander upon receipt and detection of an SAS packet (OOB) in the consumption-power saving mode. In response to the interruption, the firmware of the SAS expander switches the power supply state thereof from the consumption-power saving mode into a normal power supply mode, and thereby activates (Wakes up) all the disks and the entire SAS expander in the DE.
A typical SAS cable that connects SAS ports is made of Copper (hereinafter, such a cable is referred to as a Copper cable) while also an Active Optical Cable (AOC cable) has been recently used as a SAS cable. For the above, an SAS expander (expander chip) has dealt with an AOC cable as well as a Copper cable.
The specification of a Copper cable is different from that of an AOC cable. For the above, the firmware of an SAS expander specifies the type of the SAS cable (here whether the SAS cable is a Copper cable or an AOC cable), and changes the setting of an SAS port on the expander chip in accordance with the type of an SAS cable. Unless a correct setting in accordance with the type of an SAS cable is set for the SAS port, the SAS expander does not successfully receive an SAS packet for activation interruption and consequently does not restore the power supply state from the consumption-power saving mode to the normal power supply mode.
For example, when an SAS cable has been hot-swapped from a Copper cable to an AOC cable, the monitoring function of the firmware of the SAS expander detects a change in the mounting state of the SAS cable (unplugging and plugging of a cable). Detection of a change in the mounting state of the SAS cable causes the firmware to specify the type of the replacement SAS cable and changes the setting of the SAS cable in accordance with the specified type.
In contrast, when an SAS cable has been cold-swapped from a Copper cable to an AOC cable after the SAS expander is switched into the consumption-power saving mode by the above function of Wake on SAS, the functional elements of the SAS expander except for the activation interruption receiver are in the off state. Under this state, the SAS expander is not allowed to change the setting of the SAS cable. Furthermore, the SAS expander is incapable of receiving an SAS packet (OOB) as activation interruption even if the activation interruption receiver is in the resident state, so that the SAS expander would be fallen into a dead-lock state where the above function of Wake on SAS is incapable of activating the DE.